Efficient measuring apparatuses for electric components are a necessary and important tool for the electric and electronic industry and have been improved over time. Examples of such measuring apparatuses are the HP 4192A LF Impedance Analyzer and the HP 4278A 1 kHz/1 MHz Capacitance Meter manufactured and sold by Hewlett-Packard Company, U.S.A. Devices measured by such measuring instruments include both polar and nonpolar devices and are often measured while under DC (direct current) bias condition. As an example, the capacitance of diodes, especially of varacter diodes should be measured as a function of the DC voltage applied to the diodes. FIG. 3 shows a prior art measuring instrument for varactor diodes.
AC (alternating current) signal source 1 for measurement applies AC voltage for measurement to one terminal of a polar device (varactor diode) 5 via capacitor 2. Variable DC supply 16 superimposes DC bias voltage on terminal 3 through resistor 15 and inductor 14. A non-inverting input terminal 8 of high gain amplifier 6 is grounded and inverting input terminal 7 is connected to both output terminal 10 of amplifier 6 via resistor 9 and terminal 4 of polar device 5, such that terminal 4 is virtually grounded and current flowing through device 5 is input to resistor 9. Voltage V3 on terminal 3 is fed into vector ratio calculating means 13 via terminal 11 and switch 12. Alternately, voltage V10 on terminal 10 is also fed into vector ratio calculating means 13 via switch 12.
Vector ratio calculating means utilizes a well known method to calculate impedance Z5 of device 5 according to the following equation: EQU Z5=(V3/V10).times.R9
where R9 is value of resistor 9. The output voltage value of variable direct current source 16 is set by microcomputer 17 via wiring 19. The voltage value to be set is input to microcomputer 17 from external switches or bus 18.
In this measuring apparatus device 5 should be connected across terminal 3 and terminal 4 according to the predetermined polarity. If the device 5 is connected incorrectly, the measured values will be erroneous. Consequently, in the prior art, device polarity needs to be determined prior to measurement. Frequently in chip device measurement, no advanced polarity settings are available, resulting in long measurement times, which are inefficient. Also, the need to determine polarity prior to measurement requires the use of separate equipment.
As has been described, by implementing this invention, a polar device can be connected to a measuring apparatus without regard to its polarity and measured without error. The invention is very useful in this field.